A worm is a small animal with a long, thin body, no bones, and no legs.

A worm is a computer program that contains a virus which duplicates itself many times in a network.

If you say that someone is opening a can of worms, you are warning them that they are planning to do or talk about something that is much more complicated, unpleasant, or difficult than they realize and that might be better left alone.

If you say that someone is worming their way to success, or is worming their way into someone else's affection, you disapprove of the way that they are gradually making someone trust them or like them, often in order to deceive them or gain some advantage.